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  <meta charset="UTF-8">
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  <title>Document</title>
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<body>
  
</body>
<script>
  window.onload = function() {
    var arr = [8,19,3,12,5,4];
    function myFun(arr) {
      // 外层循环控制比较多少轮
      for(var i=0;i<arr.length-1;i++) {
        // 内层循环控制每次循环比较几个元素
        for(var j=0;j<arr.length-i-1;j++) {
          if(arr[j] > arr[j+1]) {
            var temp = arr[j];
            arr[j] = arr[j+1];
            arr[j+1] = temp;
          }
        }
      }
      return arr;
    }
    console.log(myFun(arr));
  }
</script>
</html>